The invention relates to a device for preventing the transitory reclosing of the contacts of a current limiting circuit breaker after opening by electrodynamic repulsion caused by a short circuit current before the current is extinguished. Interruption of the short circuit current can be due to two distinct causes: namely, a transitory rapid contact separation, or by the positive operation of the circuit breaker trip mechanism to hold the contacts open indefinitely.
In current limiting circuit breakers, the two arms bearing the contacts are free to separate due to electrodynamic repulsion under intense short circuit currents. Opening of the contacts is subsequently completed by the circuit breaker operating mechanism, if the short circuit current is maintained for a time sufficiently long enough to articulate the operating mechanism.
The high separation speed of the contacts necessary to provide the current limitation can result in a rebound of the contacts upon separation resulting in a transitory reclosing of the contacts before the operating mechanism has had sufficient time to operate. When the short circuit occurrence is shorter than the response time of the operating mechanism, there is no need to open the contacts indefinitely. It is important however, to ensure continuity of circuit current in the absence of a real fault condition. With 3-phase loads protected by 3-pole breakers, it is essential to prevent a single-phase transitory short circuit occurrence from opening only one pole of the breaker, resulting in a dangerous condition known as "single phasing".
The purpose of this invention is to delay reclosing of the circuit breaker contacts, after a short circuit interruption, for a period of time sufficient to allow the operating mechanism to open the contacts indefinitely providing the short circuit lasts for a time longer than the delay.